We learned Terry Shaffer will retire officially on December 23. The department is he heads is currently under a TBI investigation.

District Attorney General Barry Staubus would not comment on the exact nature of the investigation, but did tell News 5 it deals with irregularities within the highway department. "The information came to me and as a result of that I asked that an independent investigation be done by the Tennessee Bureau of Investigation, that investigation is ongoing," said Barry Staubus, the Sullivan County District Attorney.

Staubus tells us the investigation should be complete by February.

Shaffer was appointed as interim commissioner by Sullivan County Mayor Steve Godsey in February 2011, following the conviction of then-highway commissioner Alan Pope on official misconduct charges.